Power transmission to or from a fluid



April 30, 1940. c. 0. J4 MONTELIUS 2,198,786

POWER TRANSMISSION TO OR FROM A FLUID Filed May 5, 1957 /2 H INVENTORL CARL. O6CAR JO5EF' MONTELIU6 mz zb g ATT RNEYJ Patented Apr. 30, 1940 POWER TRANSMISSION TO OR FROM A FLUID Carl Oscar Josef Montelius, Stockholm, Sweden, assignor to Aktiebolaget Imo-Industri, Stockholm, Sweden, a corporation of Sweden Application May 5, 1937. Serial No. 140,875 In Sweden February 7, 1935 2 Claims.

In United States Patent No. 1,698,802 a power transmission to or from a fluid is disclosed which may be used as pump, compressor, motor or meter and which comprises a number of intermesh ing revoluble screws disposed in a housing fitting to the outside perimeter of the screws, the cooperating helical surfaces of the thread of the screws being each generated by the outer edge line of the helical surface of the adjacent screw and the helical surfaces of the thread of the one screw being substantially convex whereas those of the co-operating screw being substantially concave.

In United States Patent No. 1,821,523 an improvement of this device is disclosed according to which the outer edge of the thread of the screw having concave helical surfaces is shaped as a rolling surface bearing against the root of the thread of the screw having convex helical surfaces.

The present invention relates to .an improveof Fig. 1.

ment of the device disclosed in the above said root of the thread but rounded towards the top of the thread.

. Still another object of the invention is to provide a device of the class described in which the convex helical surfaces of the one screw bear not. 7 on the outer edge of the intermeshing screw but on a rounded part on thehelical surfaces of said screw, whereas the concave helical surfaces of the thread of the latter screw bear on the outer edge of the helical surfaces of the thread of the former screw.

A still further object of my invention is to provide a device of the class described having at least a pair of intermeshing and cooperating revoluble screws one of which is a power screw and has a convex helical surfaces and the other an idle screw having helical surfaces which are concave towards the root of the thread and rounded towards the top of the thread.

These and further objects of the invention will be apparent according as the following description proceeds reference being had to the accompanying drawing showing by way of example some embodiments thereof.

In the drawing:

Figures 1 and2 are cross-sectional views of screw sets according to the invention;

Figure 3 is a cross sectional view on an enlarged scale of a part of the screw set shown in Fig. 2; and a Figure 4 is a modification of Fig. 3.

i In Fig. 1 reference numeral l0 designates a single-thread power screw and l I a double-thread idle screw. Screw I0 is provided with convex helical, surfaces 1 2, the outer edges of which have 10 a relatively short rounded portion I 3, whereas the idle screw I I has helical surfaces which within a given diameter have a concave part l4 and outside said diameter a relatively short rounded part I5. I

In Fig. 2, reference numeral designates a power screw cooperating with two double-thread idle screws 2|, the helical surfaces of the screws being formed in accordance with the description 20 Fig. 3 illustrates how the contact between the helical surfaces of the screws takes place in Fig. 2. The convex'helical surface I2 of the power screw In is shaped to engage with the rounded part ill of the helical surface of the idle screw I, whereas the Concave part M of the helical surface of the idle screw H is shaped to engage with the I outer edge 13 of the helical surface of the power 1 screw In. On rotation of the screws the point 25 i on the outer edge I3 of the outer cylindric sur- 'face of the power screw will come into contact with the point 25' close to the root of the thread of the idle screw, then an adjacent point 26 on the power screw with the point 25' on the idle J screw and the point 21 on the power screw with the point 21 on the idle screw. In similar manner the points 21, 28' and 29' on the rounded part of the idle screw adjacent the outer edge of said screw will one after the other come in contact with the points 21, 28, 29 on the power screw.

Amongst all said points only points 29 and 29' are situated on the same or substantially the same distance from the axis of rotation of corresponding screws. On the rotation of the screws the points 29 and 29' will, thus, touch each other without sliding or at least without any essential Sliding. whereas all other points have a considerable sliding motion. When now the screws are exactly manufactured so that real contact occurs at all said points, that is between points 25, 26, 21, 28, 29 and intermediate points on. the power screw and points 25, 26', 21', 28', 29' on the idle screw no or only a slight wear will occur at the points 29 and 29' but, on the contrary, a more or less considerable wear at other points. Due

to the wear a small play is formed along the whole helical surfaces except at the points 29 and 29' where contact still takes place. Thus, the screws tend to grind themselves to the ideal state in which contact only takes place at these points at which the friction is smallest.

By the convex helical surfaces of the power screw l0 fitting tightly to the rounded part ll) of the helical surface of the idle screw II the contact between the screws takes place on a sur-" face and not along a line causing a considerable reduction in the leakage which is always'to be considered in devices of this type.

As it meets with certain difficulties to' manufacture the helical surfaces with such an exactness that only the points 29 and 29' are in contact with each other and the helical surface 21, 28, 29 fits exactly and without friction to the outer edge of the idle screw the above mentioned condition is according to the invention utilized for the manufacture of the screws in such manner that the screws are manufactured only with approximately exact shape or rounding, for instance in such a manner that the surface N5 of the helical surface of the idle screw is barely in contact with'the helical surface I2 of the power screw, the rounding of the surface I5 being effected by grinding against said helical surface l2.

Fig. 4 illustrates how such a grinding appears. Before the grinding the idle screw H has the shape designated by the line l822-l5l4, and after the grinding it has assumed the ideal shape above described designated by the line l8-l5'l 4 which is manifested by the helical surface of the thread of the screw having been worn adjacent its outer edgealong the width l8l5.

According to Fig. 3 the outer edge l6 of the idle screw is rounded corresponding to a similar sur- 4( face I? on the power screw. However, the edge of the idle screw may also be acute as shown at I8 in Fig, 4 in which case the power screw must, of course, be shaped in a corresponding manner as shown at I9. 45 What I claim is:

1. In a screw engine or the like for power transmission to or from a fluid,having at least two intermeshing and cooperating rotatable screws, and a casing surrounding and fitting the 0 outside perimeter of said screws, the feature of having one screw driving and transmitting the main portion of the power and provided with convex helical surfaces upon the thread thereof and the other screw driven and meshing with'the first screw simply as a sealing means, the helical surfaces of the thread of said other screw being concave towards the root of the thread and rounded'out towards the top of the thread with the concave portion forming a relatively long curved contact portion and the rounded out portion directly connected thereto and forming a relatively short convexly curved contact portion, whilethe convex helical surfaces of the thread of said one screw are convexly curved towards said top of the thread with a relatively short curved contact portion making contact with the relatively long curved contact portion of said other or concave screw so that positive contact,

occurs between the outer edge of the convex helical surface of said one screw and the concave portion of the other screw at a point where friction is at minimum.

2. In a screw engine or the like for power transmission to or from a fluid, having at least one driving screw and one driven screw intermeshing and cooperating together, and a casing surrounding and fittingthe outside perimeter of said screws, the feature of having the helical surfaces of the thread of the driven screw concave towards the root of the thread and rounded opt towards the top of the thread with the con ye portion forming a relatively long curved 09?, act portion and the rounded out portion directly connected thereto and forming a relatively short convexly curved contact portion, and having the helical surfaces of the thread of the intermeshing driving screw convex and curved towards the top of the thread with a relatively short curved contact portion adapted to fit and co-act with the relatively long curved contact portion of said driven screw, and with a relatively long convexly. curved contact portion directly connected to the relatively short contact portion of said driving screw making contact with the relatively short curved contact portion adjacent to the top of the thread of the driven screw so that positive contact occurs between the screws at a point where friction is at minimum.

CARL OSCAR JQSEF MONTELIUS. 

